Devouring junk food in times of anxiety may not be exclusive to college students. In the recent online edition of Physiology and Behavior, Emory University researchers at the Yerkes National Primate Research Center discovered that socially subordinate female rhesus monkeys consume more calorie-rich foods than do their dominant counterparts. Not only does this study offer valuable insight on the psychological basis for the rising trend in obesity, but it also demonstrates how food consumption can be measured in optimal animal models.

The team, led by principal investigator Mark Wilson, chief of the Division of Psychobiology at Yerkes, wished to determine whether chronic exposure to psychologically stressful environments correlates with over-consumption of high-calorie foods. The Yerkes team decided to research the feeding patterns of housed rhesus macaques, in which the dominant macaques maintain a social hierarchy through ongoing harassment and aggression. As a result, subordinate females undergo continual psychological stress.

Over the course of the study, scientists introduced a sweet, low-fat diet and a high-fat diet for 21 days each. In the three-week period between each type of test diet, the macaques had access only to standard monkey chow. A tracking device implanted in the animal's wrist allowed researchers to record whether the automated feeder dispensed a low-fat or high-fat pellet. Results showed that socially subordinate females devoured drastically more of both the low- and high-fat diets throughout a 24-hour time course. In contrast, socially dominant females consumed far less food and limited their feedings to daytime periods.

Accelerated feeding inevitably led to weight gain and accumulation of fat-derived hormones for subordinate females. Wilson explained, "Subordinates may be on a trajectory for metabolic problems. As this study shows, they prefer the high-fat diet and, as a result of the stress of being a subordinate, they have higher levels of the hormone cortisol. This may be involved in the redistribution of fat to visceral locations in the body, something that is clinically associated with type II diabetes metabolic syndrome."

Seeking the underlying neurochemical mechanisms that may induce overeating, Wilson and his research team will next use neuroimaging techniques to observe brain differences in the experimental groups. Particularly, they wish to determine whether appetite signals and reward centers of the brain differ between socially subordinate and dominant female macaques. This initial finding by Wilson's team serves as a promising precursor for understanding the expansive field of neurophysiology.